And as we reported, the terror threat has prompted the closure of embassies and koconsulates across africa and the arab world. The biggest mass closing since 9/11. Abc's nick schifrin is at the center of those closures, cairo, egypt, tonight. Reporter: At embassy after embassy, buildings supposed to be open and busy, now fortresses. In yemen, the source of the threat, soldiers guard embassy walls, check cars and pat down visitors. In all, every single embassy or consulate in the arab shut across 7,000 miles. Some of them shut through the 10th. And tonight, four new countries added to the list. All in africa, none of them primarily muslim. The state department saying they'll be closed out of a, quote, abundance of caution. And in the middle of the map, egypt. In the last few years, the u.S. Has spent billions to boost embassy security. Increasing the distance between the building and the street. In other places, beefing up perimeter defenses. Many embassies can withstand explosions. The new london embassy will have a moat. And these pylons can disable truck bombs. And since the benghazi siege, 500 soldiers and marines on a new quick reaction force. And though not yet deployed, 1,000 additional marines for embassy security. The state of the world does require more security. Reporter: Few know threats to diplomats more than ronald newman. He served in lebanon, afghanis afghanistan. BACK IN THE '80s, HIS SECURITY Was a locked door and his own shotgun. The threats are bigger, the attacks have been bigger and there's more security available. Reporter: And for americans traveling, many keeping their heads down. I can. And that said, I don't walk into harm's way intentionally. Avoid large crowds where I can. Reporter: And tonight, the fact that these embassies will stay closed all week shows just how seriously u.S. Officials consider this threat.

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